Method for calibrating tilt of actuator by offsetting control voltage

ABSTRACT

A method for calibrating a tilt of an actuator includes the following steps: focusing a light beam projected from an objective lens onto a data layer of an optical disc; utilizing a digital signal processor to output control voltages through an analog driving circuit for driving the actuator to tilt the objective lens, and accordingly recording corresponding displacement signals of the objective lens; fitting a tilt curve through the recorded control voltages and the displacement signals; utilizing the digital signal processor to output a zero control voltage, not through the analog driving circuit, for tilting the objective lens, and accordingly measuring a standard displacement signal; acquiring a bias voltage from the tilt curve according to the standard displacement signal; and calibrating the tilt of the actuator by offsetting a control voltage outputted from the digital signal processor according to the bias voltage for controlling the analog driving circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disc drive, and moreparticularly, to a method for calibrating a tilt of an actuator in apick-up head of an optical disc drive, where the actuator is used tomove an objective lens.

2. Description of the Prior Art

With the trend toward the compact and light-weight consumer electronicproducts, an error of a driving signal of an actuator is magnified dueto a light pick-up head of an optical disc drive, resulting in a largertilt amount of an objective lens. This may further affect the read/writeaccuracy of the optical disc drive.

Please refer to FIG. 1, which is a block diagram illustrating aconventional design of calibrating a tilt of an actuator. A conventionaloptical disc drive 10 uses a microprocessor 11 for controlling a spindlemotor 12 to rotate an optical disc 13, and controlling a digital signalprocessor (DSP) 14 to convert a digital control signal into an analogcontrol voltage. The analog control voltage is transmitted through ananalog driving circuit 15 to drive an actuator 16 of a pick-up head toascend/descend or tilt an objective lens 17 along a vertical or radialdirection of the optical disc 13 for a servo control, such as a focusingor tracking control.

However, as the control voltage outputted from the DSP 14 is transmittedthrough the analog driving circuit 15 to drive the actuator 16, there isan error in the output level of the control voltage due to theelectrical characteristics (e.g., the impedance) of the analog drivingcircuit 15. As a result, the control voltage fails to move the objectivelens 17 to the desired location precisely, which affects the read/writequality of the optical disc drive. In addition, the objective lens 17may move even beyond the maximum allowable range to crash the pick-uphead. Therefore, regarding the actuator motion error, the conventionaldesign has a calibration problem remained unsolved.

SUMMARY OF THE INVENTION

It is one objective of the present invention to provide a method forcalibrating a tilt of an actuator. A tilt curve is fitted through tiltmotions of the actuator driven by a plurality of control voltages. Abias voltage is acquired from the tilt curve according to a standarddisplacement signal that is not obtained through an analog drivingcircuit, and then is used to calibrate the tilt of the actuator.

It is another objective of the present invention to provide a method forcalibrating a tilt of an actuator. By offsetting a control voltageoutputted from a digital signal processor according to a bias voltage,the actuator is driven precisely and thus the read/write quality isimproved.

In order to achieve the above objectives, the present invention providesa method for calibrating a tilt of an actuator. The method forcalibrating the tilt error of the actuator includes the following steps:focusing a light beam onto a data layer; outputting a plurality ofcontrol voltages through an analog driving circuit for driving theactuator to tilt an objective lens, and accordingly recordingcorresponding displacement signals (e.g., central error signals) of theobjective lens; fitting a tilt curve (e.g., a linear curve); outputtinga zero control voltage, not through the analog driving circuit, fortilting the objective lens, and accordingly measuring a standarddisplacement signal; acquiring a bias voltage from the tilt curveaccording to the standard displacement signal; and offsetting theplurality of control voltages to calibrate the tilt of the actuator.

In the present invention, the digital signal processor outputs the zerocontrol voltage that is not transmitted through the analog drivingcircuit by turning off the analog driving circuit or setting the analogdriving circuit in a high impedance mode. A difference value between thestandard displacement signal and a displacement signal corresponding tothe zero control voltage on the tilt curve is a tilt error generatedfrom tilting an objective lens. The standard displacement signal issubstituted into the tilt curve to obtain a correspondent standardcontrol voltage, which is an error voltage outputted through the analogdriving circuit when the digital signal processor outputs the zerocontrol voltage, and the standard control voltage is used as the biasvoltage.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a conventional design ofcalibrating a tilt of an actuator.

FIG. 2 is a block diagram illustrating an exemplary design ofcalibrating a tilt of an actuator according to an embodiment of thepresent invention.

FIG. 3 is a fitted tilt curve according to an embodiment of the presentinvention.

FIG. 4 is a flowchart illustrating a method for calibrating a tilt of anactuator according an embodiment of the present invention.

DETAILED DESCRIPTION

With regard to technical means and utilities thereof used to achieve theabove objectives of the present invention, preferred embodiments aredescribed as follows by way of examples and with reference to theaccompanying diagrams.

Please refer to FIG. 2 together with FIG. 3. FIG. 2 is a block diagramillustrating an exemplary design of calibrating a tilt of an actuatoraccording to an embodiment of the present invention, and FIG. 3 is afitted tilt curve according to an embodiment of the present invention.In FIG. 2, an exemplary method for calibrating the tilt of the actuator20 according to the embodiment of the present invention mainly focuseson performing a calibration upon a radial tilt of the actuator 20.During the calibration performed upon the tilt of the actuator 20, inorder to reduce the interference generated from driving the actuator 20to move an objective lens 21 up and down, the actuator 20 may be drivento move the objective lens 21 up and down first, thus making a lightbeam projected from the objective lens 21 focused onto a data layer 23of an optical disc 22. Next, a control signal is outputted for drivingthe actuator 20 to tilt the objective lens 21, and a digital signalprocessor 24 may convert the control signal (in the digital form) into acontrol voltage V (in the analog form). The control voltage V is fedthrough an analog driving circuit 25 for driving the actuator 20 to tiltthe objective lens 21 such that the objective lens 21 moves along aradial direction of the optical disc 22. The optical disc drive maymonitor an actual tilt amount of the objective lens 21 by detecting adisplacement signal corresponding to the motion of the objective lens 21(e.g., a central error (CE) signal) or a signal obtained from measuringa reflected light spot position of the objective lens 21 in an opticalsensor. In this embodiment, the central error signal is taken as anexample of the displacement signal, the central error signal representsa radial distance between the objective lens 21 and a central point C ofthe actuator 20, and the actual tilt amount of the objective lens 21 isacquired from monitoring the central error signal.

When the digital signal processor 24 outputs the control voltage V, anerror is generated in the tilt amount of the objective lens 21 becausethe control voltage V is fed through the analog driving circuit 25 fordriving the actuator 20 to tilt the objective lens 21. No standard tiltamount of the objective lens 21 may be referenced to obtain a correctedtilt amount of the objective lens 21. Therefore, as shown in FIG. 3, thepresent invention utilizes the digital signal processor 24 to output aplurality of control voltages through the analog driving circuit 25 fordriving the actuator 20 to tilt the objective lens 21, and accordinglyrecords corresponding displacement signals. In addition, measured dataare marked in the central error signal (CE) versus control voltage (V)graph to fit a tilt curve L of the actual tilt amount of the objectivelens 21. Please note that the tilt curve L shown as a linear curve isfor illustrative purposes only. For example, the same objective of thepresent invention is achieved by using a non-linear curve (e.g., asecond-order curve or a third-order curve) as the tilt curve L.

Considering a case where the digital signal processor 24 outputs a zerocontrol voltage (i.e., V=0), if the zero control voltage does not passthrough the analog driving circuit 25, the tilt amount of the objectivelens 21 is not affected by the analog driving circuit 25, and thus thereis no error generated therein. As a result, the present inventionutilizes the digital signal processor 24 to output the zero controlvoltage, not through the analog drive circuit, by turning off the analogdriving circuit 25 or setting the analog driving circuit in a highimpedance mode, thus avoiding the generated error of the tilt amount.Next, a standard central error signal A is measured. A difference valueΔCE between the standard central error signal A and a central errorsignal corresponding to the zero control voltage on the tilt curve L isa tilt error generated from tilting the objective lens 21 by theactuator 20. A standard control voltage V0 corresponding to the standardcentral error signal A may be acquired from the tilt curve L bysubstituting the standard central error signal A into the tilt curve L,wherein the standard central error signal A is generated without beingeffected by the analog driving circuit 25. The standard control voltageV0 is regarded as a control voltage corrected by the difference valueΔCE, and is an error voltage outputted through the analog drivingcircuit 25 when the digital signal processor 24 outputs the zero controlvoltage. As the standard control voltage V0 may be regarded as anaverage error voltage outputted through the analog driving circuit 25,the standard control voltage V0 is used as a bias voltage outputted fromthe digital signal processor through the analog driving circuit 25. Forexample, in a case where a value of the CE signal is measured as 914 bysetting the analog driving circuit 25 in a high impedance mode, thestandard control voltage V0 acquired from the tilt curve L is −22, whichis taken as an offset value of the control voltage outputted from thedigital signal processor 24. Therefore, the present invention calibratesthe tilt of the actuator 20 by offsetting the control voltage outputtedfrom the analog driving circuit 25 according to the standard controlvoltage V0.

FIG. 4 is a flowchart illustrating a method for calibrating a tilt of anactuator according an embodiment of the present invention. The steps ofthe exemplary method are described in detail as follows. First, in stepS1, the flow focuses a light beam projected from an objective lens ontoa data layer of an optical disc. In step S2, the flow utilizes a digitalsignal processor to output a plurality of control voltages through ananalog driving circuit for driving the actuator to tilt the objectivelens. In step S3, the flow records corresponding displacement signals ofthe objective lens in sequence. In step S4, the flow fits a tilt curvethrough the recorded control voltages and the corresponding displacementsignals. Next, in step S5, the flow turns off the analog drivingcircuit, or sets the analog driving circuit in a high impedance mode,and utilizes the digital signal processor to output a zero controlvoltage, not through the analog drive circuit, for driving the actuatorto tilt the objective lens. In step S6, the flow measures a standarddisplacement signal. In step S7, the flow acquires a correspondentstandard control voltage from the tilt curve according to the standarddisplacement signal, and the correspondent standard control voltage isused as a bias voltage. Finally, in step S8, the flow offsets thecontrol voltage outputted from the digital signal processor according tothe standard control voltage for controlling the analog driving circuit,thereby calibrating the tilt of the actuator.

Therefore, the exemplary method for calibrating a tilt of an actuatorfirst fits a tilt curve of the actuator through tilt motions of theactuator and corresponding displacement signals, wherein the actuator isdriven by a plurality of control voltages outputted from a digitalsignal processor. Next, a standard displacement signal is measured undera condition where an analog driving circuit is turned off or set in ahigh impedance mode. The standard displacement signal is substitutedinto the tilt curve to obtain a correspondent standard control voltage,and the standard control voltage is used as a bias voltage to offset thecontrol voltage outputted from the digital signal processor. Therefore,the actuator is driven precisely, and the objective of calibrating thetilt of the actuator is achieved.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for calibrating a tilt of an actuator, comprising: (a)focusing a light beam projected from an objective lens onto a data layerof an optical disc; (b) utilizing a digital signal processor to output aplurality of control voltages through an analog driving circuit fordriving the actuator to tilt the objective lens, and accordinglyrecording corresponding displacement signals of the objective lens; (c)fitting a tilt curve through the recorded control voltages and thedisplacement signals; (d) utilizing the digital signal processor tooutput a zero control voltage, not through the analog driving circuit,for tilting the objective lens, and accordingly measuring a standarddisplacement signal; (e) acquiring a bias voltage from the tilt curveaccording to the standard displacement signal; and (f) calibrating thetilt of the actuator by offsetting a control voltage outputted from thedigital signal processor according to the bias voltage for controllingthe analog driving circuit.
 2. The method for calibrating the tilt ofthe actuator of claim 1, wherein the digital signal processor outputsthe control voltage, not through the analog driving circuit, by settingthe analog driving circuit in a high impedance mode.
 3. The method forcalibrating the tilt of the actuator of claim 1, wherein the digitalsignal processor outputs the control voltage, not through the analogdriving circuit, by turning off the analog driving circuit.
 4. Themethod for calibrating the tilt of the actuator of claim 1, wherein eachof the displacement signals is a central error signal.
 5. The method forcalibrating the tilt of the actuator of claim 1, wherein a differencevalue between the standard displacement signal and a displacement signalcorresponding to the zero control voltage on the tilt curve is a tilterror generated from tilting the objective lens.
 6. The method forcalibrating the tilt of the actuator of claim 5, wherein the standarddisplacement signal is substituted into the tilt curve to obtain acorrespondent standard control voltage, and the standard control voltageis an error voltage outputted through the analog driving circuit whenthe digital signal processor outputs the zero control voltage.
 7. Themethod for calibrating the tilt of the actuator of claim 6, wherein thestandard control voltage is used as the bias voltage for offsetting thecontrol voltage outputted from the digital signal processor.
 8. Themethod for calibrating the tilt of the actuator of claim 1, wherein theactuator tilts the objective lens along a radial direction of theoptical disc.
 9. The method for calibrating the tilt of the actuator ofclaim 1, wherein the tilt curve is a linear curve.